There are come caveats associated with eccentric training. The extensive muscle fiber damage it produces leads to a few temporary metabolic derangements. For example, it inhibits the activity of a glucose carrier in muscle called GLUT-4, which delays the full recuperation of muscle because glycogen is not restored. Glycogen repletion is essential for full muscle recovery between workouts. In practical terms, it would be foolhardy to attempt to train any particular muscle again in less than 48 hours. If you truly emphasize negative work in your training, it will probably lengthen the required rest time between workouts to at least 72 hours. That may explain the recent trend of training most muscles groups only once a week. Many have found that more-frequent training leads to stalled progress and a feeling of overtraining, which may be related to incomplete repair of muscles that are trained too frequently.